Investigations into the cause of Alexander Dale Oen's death in Flagstaff, last Monday may take some time before proper conclusions can be made, police in Arizona said at a press conference.

The autopsy conducted on Tuesday found no evidence of how he died, the Arizona Republic newspaper reported. "The initial autopsy revealed no anatomic cause of death and no trauma associated with the death," Barbara Worgess, a chief health officer for the Coconino County Public Health Services District, said in a statement.

Investigators were running additional tests and consulting with a cardiovascular pathologist, the newspaper said.

No signs of criminal activity were found after teammates found the world 100m breaststroke champion unconscious in his hotel room at the Embassy Suites on South Milton Road, Flagstaff, just before 8pm. Dale Ooen had had a light swim and played a round of golf that day.

"We're a team of 26 people here and we have been in Flagstaff for three weeks and we expected to go home tomorrow with all of the team," Ola Roensen, the Norwegian Olympic Team's Chief Medical Officer, told the press conference.

Dale Oen's regime had not been too harsh: he was on a relatively light work load during rehabilitation for a shoulder injury, the doctor said. Neither was he on any medications, nor had he been suffering from any illness.

Cardiac arrest was cited by the Norwegian swim federation on Tuesday but the doctor noted that there were no details about the cause of death at this point.

"At this time the investigation has revealed no evidence of foul play or suspicious activity," said Acting Chief of Police Kevin Treadway. "The medical examiner's office has not released a cause of death, and their investigation may take some time."

An autopsy was performed by the Coconino County Medical Examiner's office yesterday. Petter Loevberg, performance head of Norwegian swimming, told police that he was unaware of any medical conditions the swimmer might have had. He had seen Dale Oen just 30 minutes before the swimmer was found in a collapsed state.

"Coach Loevberg also stated that Alexander does not drink, take drugs, or use any type of harmful substances," the autopsy report said. Police found nothing suspicious in the bathroom.

A police report stated that Dale Oen had complained of being cold after he returned from golf, several team members reporting that as the reason why he had taken a shower to warm up at just after 7.30pm.

The report stated he had done only a light workout on Monday and played golf. "Alexander is typically high energy, but he was acting somewhat lethargic and complaining of being cold," a teammate told police. Another teammate said he seemed "out of sorts".

Dr Roensen said that he hadn't noticed anything unusual about Dale Oen's demeanour and the swimmer had planned to dine with the team that evening as usual.

Two teammates watched TV in Dale Oen's room while he showered but after 20 minutes or so became concerned that he had not reappeared, according to the police report.

One teammate, having got no response when he knocked on the bathroom door, flicked the light switch on and off to try too get a reaction before resorting to hitting a knife on the back of the door.

There is no explanation as to how they then broke the door open but once inside the bathroom they found Dale Oen had fallen out of the tub and was was slumped unconscious over the edge of the bath.

One teammate stayed with his friend while the other ran to get the doctor, who performed CPR until medics arrived.

The Norwegian Seamen's Church, a church that serves Scandinavians abroad, is due to hold a memorial for Dale Oen with his teammates and is providing pastoral care and counselling for a traumatised Norwegian squad.

"He loved coming to Flagstaff. He's been here 9 years in a row," Loevberg said of Dale Oen. "There are no words. I just miss him so much."